NACA Technical Notes

The clearance distribution in a precombustion chamber cylinder head was varied so that for a constant compression ratio of 13.5 the spherical auxiliary chambers contained 20, 35, 50, and 70 per cent of the total clearance volume. Each chamber was connected to the cylinder by a single circular passage, flared at both ends, and of a cross-sectional area proportional to the chamber volume, thereby giving the same calculated air-flow velocity through each passage. Results of engine-performance tests are presented with variations of power, fuel consumption, explosion pressure, rate of pressure rise, ignition lag, heat loss to the cooling water, and motoring characteristics. For good performance the minimum auxiliary chamber volume, with the cylinder head design used, was 35 per cent of the total clearance volume; for larger volumes the performance improves but slightly. With the auxiliary chamber that contained 35 percent of the clearance volume there were obtained the lowest explosion pressures, medium rates of pressure rise, and slightly less than the maximum power. For all clearance distributions an increase in engine speed decreased the ignition lag in seconds and increased the rate of pressure rise